1. Field of the Invention
This invention relates to a support system for a mine roof. More particularly, the invention relates to truss brackets which retain a pair of adjustable tie bars across the width of a mine roof.
2. Description of the Prior Art
In underground mining operations such as for the deep mining of coal, the unsupported rock formation above the tunnel formed in a coal seam is reinforced by roof plates retained by rib or anchor bolts against the face of the rock formation. As an alternative support system or as a supplement to the standard support system, adjustable tie bars are utilized which extend across the width of the mine roof and are supported by truss brackets.
These truss brackets are typically attached into the rock formation. The tie bar suspension systems are placed under compression to prevent the sagging of the mine roof, usually at the center of the system between brackets. The tie bars are normally rebar, standard smooth rod or cable. The hardware to retain the tie bars consists of turnbuckles, wedges and/or various header plates which are secured by anchor bolts into the rock formation above the tunnel.
One such mine roof system is illustrated in U.S. Pat. No. 3,427,811. The hardware therein consisted of a roof plate, a welded connecting link, a pair of straps, each of which was bent about a wooden block, and a turn-buckle for tightening the straps.
A need remains for a system made up of a minimum of hardware which can be easily and rapidly installed. The need further remains for a system sufficiently strong which will reduce shear loads at the various locations adjacent the hardware. The system may act to support the sagging rock formations or roof materials while maintaining a low profile to maximize roof clearance.